High-voltage insulating-bushing.



C. LE G. FORTESCUE.

HIGH VOLTAGE INSULATING BUSHING.

APPLICATION FILEI) JUNE 4, 1915.

1,217,890. Patented Feb. 27, 1917.

I0 ll I6 /4 I0 5 A5 r q h i WITNESSES INVENTOR Char/es L e G. ForfescueR5 ca. Mum-Luna. w/ snnvmom u. c.

UNITED STATES PATENT OFFICE.

CHARLES LE G. FORTESCUE, 0F PITTEBURGI-I, PENNSYLVANIA, A-SSIGNOR TOWESTING- HOUSE ELECTRIC AND MANUFACTURING CGMPANY, A COBPORATIDN'OFPENNSYL- VANIA.

HIGH-VOLTAGE INSULATING-BUSHING.

Application filed. June 4, 1815.

To all whom it may concern Be it known that 1, CHARLES Ln G. Fon rescue,a subject of the King of Great Britain, and a resident of Pittsburgh, inthe county of Allegheny and State of Pennsylvania, have invented a newand useful Improvement in High-Voltage Insulating Bushings, of which thefollowing is a specification.

My invention relates to electrical insulators, and it has specialreference to insulating structures that may be employed as bushings toinsulate high-potential conductors.

More particularly, my invention relates to insulating bushings in whichelectrostatic lines of force are precluded from concentrating upon theexternal surfaces thereof.

An ideal insulating bushing would be of such form that, in onedirection, it would be an electrical conductor, while in a transversedirection, it would be an electrical insulator. This type of bushing maybe termed an, asymmetric conductor, and one form thereof may have theproperties of an electrical conductor in an axial direction and those ofan electrical insulator in a direction perpendicular to the axis. Byproperly shaping the end portions of this type of bushing, electrostaticfield distributions externally to, and internally of, the bushing may beobtained which will insure the utilization, to a maximum degree, of theinsulating properties of the bushing. lVhile a bushing of this characteris not yet capable of being realized, my present invention provides aninsulator or an insulating bushing, the properties of which, for allpractical purposes, accord with the principles stated above. By means ofmy invention, the potential distribution on the outer surfaces of thebushing corresponds to that resulting from a uniform electrostaticfield, the equipotential surfaces of which are uniformly distributed atright angles to the axis of the bushing.

An object of my invention is to provide an insulator which may be easilyand cheaply manufactured and which is adapted for very high-voltageservice conditions. Moreover, an insulating structure embodying myinvention may be very compact and may comprise a minimum amount ofinsulating material, while, at the same time, it will preclude theformation of corona discharges upon its exposed surfaces.

Specification of Letters Patent.

Patented Feb. 27, 1917.

Serial No. 32,185.

For a better understanding of the nature and scope of my invention,reference may be had to the following description and the accompanyingdrawingin which Figure 1 is a View, partially in elevation and partiallyin section, of an insulating bushing construeted in accordance with myinvention; Fig. 2 is a. cross-sectional view of the bushing shown inFig. 1; Figs. 3 and t are plan and cross-sectional views, respectively,of a material which I may employ in my insulator; Figs. 5 and 6, andFigs. 7 and 8 are views, corresponding, respectively, to Figs. 3 and 4and illustrating the method of constructing a substitute material. forthat shown in Figs. 3 and 4; Fig. 9 is a plan. view, showing a formwhich material embodied in my insulating bushing may assume beforeperforming the wrapping operation, and Fig. 10 is a view, inperspective, showing a method of constructing my terminal bushing.

My invention embodies an insulating bushing of the characterabove-mentioned which comprises a series of conducting strands insulatedfrom one another and longitudinally disposed with respect to the axis ofthe bushing. The conducting strands are of relatively smallcross-sectional area,'and are spaced relatively small and uniform distances from one another, each strand, however, being insulated fromadjacent strands. It is desired to have the material comprising'mybushing as homogeneous as possible,

the number of conducting strands per unit area being thesame and thespacing of the strands from one another throughout the structure beinguniform. The conducting strands may be arranged in any convenientmanner, as will hereinafter be pointed out, upon a continuous sheet ofmaterial which is wound upon a mandrel simultaneously with an insulatingfabric of high dielectric strength. After the bushing has thus beenbuilt up, the ends thereof are so shaped that the conducting strands arecut to proper lengths which correspond to their spacing from the axis ofthe bushingin order that the desired distribution of potential upon theouter surfaces of the bushing may be obtained.

Referring to Fig. 1, a conducting tubular member 1 which is connected,in any convenient manner, to a high-potential conductor 2, extendsthrough an insulating bushing 3 which is built in accordance with myinvention. The insulating bushing 3 is embraced by a centrally-disposedconducting ring 4 which engages the peripheral walls of an openingformed in a member 5 from which it is desired to insulate the member 1.A dis coidal-shaped conducting body 6, having rounded edges, is disposedat the upper end of the bushing 3 in such manner that its lower surface7 is substantially parallel to the member 5.

The bushing 3 comprises a plurality of alternately disposed conyolutionsof sheet insulating material 8 and a material 9 hr-iving conductingstrands 10 which are so arranged as to lend electrical conductivitythereto in the direction of the axis of the bushing only. Eachconi'olution 11, embodied in the bushing 3, comprises a plurality of theinsulated conducting strands 10 which are longitudinally disposed withrespect to the axis of the bushing.

By referring to Fig. 2, it will be seen that, by reason of the spiralformation of the con- Volutions 11, the conducting strands 10 are spacedfrom the central conducting tube 1 'arying distances which differ fromone another by small increments. Inasmuch as the electrical potential ofeach conducting strand is dependent upon its position relative to thehigh-potential conducting lead 1, it will be apparent that thepotentials of the conducting strands will vary from one another byincrements. The layers or convolutions comprising the conducting strands10 are interposed between adjacent insulating layers or convolutions 8,the latter imparting the property to the condenser terminal 3 of beingan insulator in a direction perpendicular to the axis of the bushing.The layers 9, comprising the longitudinally conducting strands 10,impart the property to the bushing 3 of being an electrical conductor inan axial direction. In this manner, the bushing 3 corresponds, in asense, to an asymmetric conductor of the character hereinbeforeindicated.

The end portions of the bushing 3 are tapered, and the surfaces thereofare preferably so shaped as to insure a uniform potential gradient onthe external surfaces of the bushing. In accordance with the principlesdisclosed in U. S. Patents Nos. 1,129,463 and 1,129,466, granted to theestinghouse Electric & Manufacturing Com pany upon applications filed byme, a substantially uniform potential gradient upon the outer surfacesof the bushing may be established by employing the conductingdiscoidal-shaped body 6, and by properly shaping the ends of the bushing3. It may be demonstrated mathematically that, under these conditions, auniform potential distribution may be obtained by shaping the ex-'ternal surfaces of the end portions of the bushing 3 to provide a doublecurvature comprising two logarithmic curves, as indicated at 12 and 13.In this manner, a substantially uniform external electrostatic fieldenvelope the bushing 3 and thereby precludes the formation of coronadischarges at any point upon the surfaces of the bushing.

To construct my terminal bushing, reference may be had to Figs. 3, l:and 10. The layers 9 of the terminal bushing 3 comprise a plurality ofconducting strands 10, which are conveniently formed as illustrated inFigs. 3 and -il-. The conducting strands .10 are relatively small incross-section and are spaced from one another uniformly and relati relyshort distances. They may consist of tinsel threads which are interwovenwith cross threads 12, as shown in Fig. The threads 12 may be made ofsilk, asbestos, or any other insulating material which insures that eachstrand 10 will be" insulated from the strands disposed adjacentlythereto. A sheet of this material is then disposed upon a sheet ofinsulating material which may constitute the insulating layers 8 of theterminal 3. Both of these continuous sheets are then simultaneouslywound upon a central mandrel (not shown) in accordance with theprinciples set forth in Patent No. 858,385, granted July 2, 1907 to theVestinghouse Electric &- Manufacturing Company, as assignee of EmilHaefely. The form assumed by the insulating sheet and the superposedsheet comprising the conducting strands 1.0 during the winding processis illustrated in Fig. 10. It will be noted that the conducting strands10 are interposed between adjacent con olutions of insulating material 8and, moreover, that each strand is insulated and uniformly spaced fromthe other strands. After the bushing is wound up in a cylindrical form,as shown in Fig. 10, the end portions thereof may be tapered. in anyconvenient manner to conform to the shape shown in Fig. 1.

Another method of manufacturing myinsulating bushing is illustrated inFigs. 5, (3, 7 and 8. A sheet 14 of conducting material, such astinfoil, is disposed upon a sheet 15 of an insulating material whichserves as a means of support therefor. After the conducting layer 11-has been firmly attached, in any convenient manner, to the insulatingsheet 15, channels 16 are cut in the conducting sheet 1%, as shown inFigs. 7 and 8. In this manner, a plurality of con ducting strands 10 areformed each of which firmly adheres to the insulating layer 15. Thesesheets, comprising the conducting strands 10, are then wound up to forman insulating bushing in the manner explained in connection with theemployment of the fabric shown in Figs. 3 and at.

Inasmuch as the bushing 3 comprises tapering ends, the intermediateportion of which has a maximum diameter, it may be desirable to cut thesheets 14 and 15 in a manner shown in Fig. 9 before proceeding with thewinding operation. A rectangular sheet 17, having the conducting strands10 disposed thereupon, is cut into half portions 18 each of which has atrapezoidal form. One of the half portions 18 is then wound with theinsulating layer 15 in such a manner that the free end of the outermostlayer or, convolution of the central portion of the completed bushingcorresponds to the shorter side 19 of the trapezoidal portion 18. Ofcourse, it will be understood that the longer side 20 of the trapezoidalportion 18 is disposed adjacent to the central mand rel at the beginningof the winding operation. As the insulating layers and the layerscomprising the comlucting strands 10 are continuously and simultaneouslywound into spiral formation, the completed bushing will be provided withtapering ends which subsequently may be formed so as to have the propershape, as mentioned above. By this means, a large portion of thematerial, which otherwise would be wasted when shaping the end portionsof the bushing, is saved, and two bushings may be thus wound up from aquantity of material which ordinarily would be sufficient for themanufacturing of one bushing only.

While I have shown and described several embodiments of my invention, itwill be understood that I desire to be limited only by the scope of theappended claims.

I claim as my invention:

1. An insulating bushing comprising a plurality of convolutions ofinsulating material and conducting strands which are spaced from oneanother relatively short distances between adjacent convolutions of saidinsulating material.

2. An insulating bushing comprising a plurality of convolutions ofinsulating material and conducting strands which are uniformly spacedfrom one another relatively short distances between adjacentconvolutions of said insulating material, each convolution containing arelatively large number of said conducting strands.

3. An insulating bushing comprising a plurality of convolutions ofinsulating material and longitudinally disposed eonduct ing strandswhich are uniformly spaced from one another relatively short distancesbetween adjacent convolutions of said insulating material, eachconvolution containing a relatively large number of said conductingstrands.

4. An insulating bushing comprising a plurality of convolutions ofinsulating material, and interposed convolutions of material havingconducting strands which lend electrical conductivity thereto in onedirec tion only.

5. An insulating bushing comprising convolutions of sheet insulatingmaterial and interposed convolutions of sheet material having conductingstrands which lend electrical conductivity thereto in one directiononly, each convolution of said second sheet material containing aplurality of conducting strands.

6. An insulating bushing comprising convolutions of sheet insulatingmaterial and convolutions of sheet material having conducting strandswhich lend electrical conductivity thereto in one direction only, saidsecond material being interposed between adjacent insulatingconvolutions and the conducting strands being uniformly spaced from oneanother.

Y. An insulating bushing comprising convolutions of sheet insulatingmaterial and convolutions of material having conducting strands whichlend electrical conductivity thereto in the direction of the axis of thebushing only, said second material being interposed between adjacentinsulating convolutions.

S. An insulating bushing comprising convolutions of sheet insulatingmaterial and convolutions of material having conducting strands whichlend electrical conductivity thereto in one direction only, saidconvolutions being of graded lengths and the larger convolutions beingwithin the shorter convolutions.

9. An insulating bushing comprising convolutions of sheet insulatingmaterial and convolutions of sheet material having conducting strandswhich lend electrical conductivity thereto in one direction only, saidconvolutions being of unequal lengths.

10. An insulating bushing having tapering ends and comprisingconvolutions of sheet insulating material and convolutions of materialhaving longitudinally disposed conducting strands which are uniformlyspaced from one another and lend electrical conductivity in thedirection of the axis and of the bushing only.

11. An insulating bushing comprising an asymmetric conductor ofhomogeneous structure which is an electrical conductor in one directionand an electrical insulator in another direction.

12. An insulating bushing comprising an asymmetric conductor ofhomogeneous structure which is an electrical conductor in one directionand an electrical insulator in a direction transverse thereto.

13. An insulating bushing comprising a structure having a plurality ofconducting strands which are insulated and uniformly spaced relativelysmall distances from one anotherysaid structure embracing the memher tobe insulated.

14. The combination with a conductor, of an insulating bushing havingtapering ends and surrounding the conductor and comprising a pluralityof conducting strands which lend electrical conductivity thereto in onedirection only, said conducting strands being uniformly spaced from oneanother in a body of insulating material.

15. The method of constructing an insulating bushing having taperingends which consists in winding simultaneously upon a rotatable member,two continuous sheets of materials one of which is a sheet of insulating material and the other of which coinprises conducting material,each of said sheets having a form, in development, of a 15 trapezoid.

16. The method of constructing an insu- Copies of this patent may beobtained for five cents each, by addressing the Commissioner of Patents,

Washington, I). C.

